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Influential - 22 9.Outliers Outliers .Inthe residualplot,....

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22 STAT6220 9. Outliers Outliers : Data points that diverge from the overall pattern and have large residuals are called outliers. In the residual plot, look for points more than 3 s above or below the zero line. A safe rule is to discard an outlier only if it represents an error in recording, a miscalculation or a similar circumstance. Standardized residuals The residuals divided by the estimates of their standard errors. They have mean 0 and standard deviation 1. There are two common ways to calculate the standardized residual for the i th observation. One uses the residual mean square error from the model fitted to the full dataset (Standardized residuals). The other uses the residual mean square error from the model fitted to the all of the data except the i th observation (Studentized residuals)
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23 STAT6220 Influential Points Influential points are data points with extreme values that greatly affect the slope of the regression line. Influential points should be investigated.
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